Practice!

Sample Problem

A block weighing (Fg) 35 N is resting on a steel table (µs = 0.40) .

The minimum force to start this block moving is N.

Solution

In the vertical direction, the normal force must be equal and opposite to the weight down. Thus:

N = W = 35 N

To start the block moving, a force is needed to overcome the friction.

fs = μs FN

Fmin = 0. 40 × 35 N = 14 N